1. Field of the Invention
The present invention relates to a liquid discharge head for recording on a recording medium by discharging liquid droplets, such as ink droplets. The invention also relates to the method of manufacture therefor. More particularly, the invention relates to a liquid discharge head that performs ink jet recording.
2. Related Background Art
The ink jet recording method is one of the so-called non-impact recording methods. The ink jet recording method is capable of performing high-speed recording, and the noises, which are generated at the time of recording, are as small as almost negligible. Also, the ink jet recording method makes it possible to record on various kinds of recording medium, and fix ink on a plain sheet without any particular treatment given thereto. Further, with this method, highly precise images can be obtained at lower costs. With these advantages, the ink jet recording method has been used not only as a printer serving as a peripheral device of a computer, but also, in recent years, it has been used rapidly and widely as recording means for a copying machine, facsimile equipment, a work processor, and the like.
As the ink discharge methods generally utilized for ink jet recording, there are the one that adopts electrothermal converting element, such as heater, as element for generating discharge energy used for discharging ink droplets, and the one that uses piezoelectric element, such as piezo-element. With either method, it is possible to control the discharge of ink droplets using electric signals. The principle of the ink discharge method that uses electrothermal converting element is that by the application of voltage to the electrothermal converting element, ink in the vicinity of the electrothermal converting element is boiled instantaneously to discharge ink at high speed by the abrupt development of bubble generated by the phase change of ink taking place as it is boiled. On the other hand, the principle of the ink discharge method that uses piezoelectric element is that by the application of voltage to the piezoelectric element, the piezoelectric element is displaced to discharge ink droplets by the pressure exerted when such displacement takes place.
Then, for the ink discharge method using the electrothermal converting element, there is no need for securing a large space for the arrangement of the discharge energy-generating element. Therefore, it has such advantages as to make the structure of the liquid discharge head simpler, and also, to make it easier to effectuate a higher integration of nozzles, among some others. On the other hand, this ink discharge method characteristically has weakness in that the heat and others, which are generated by the electrothermal converting element, are accumulated in the liquid discharge head to cause the volumes of flying ink droplets to vary; the cavitation resulting from bubble extinction may produce unfavorable effect on the electrothermal converting element; and the air dissolved into ink may become remaining bubbles in the liquid discharge head. Such weakness may exert unfavorable influence on the discharge characteristics of ink droplets or the quality of recorded images in some cases.
In order to solve these problems, there have been proposed the ink jet recording methods and ink discharge heads in the specifications of Japanese Patent Application Laid-Open No. 54-161935, Japanese Patent Application Laid-Open No. 61-185455, Japanese Patent Application Laid-Open No. 61-249768, and Japanese Patent Application Laid-Open No. 04-10941. In other words, the ink jet recording methods disclosed in the aforesaid specifications are structured so that bubbles generated by driving the electrothermal converting element by means of electric signals are communicated with the air outside. With the adoption of such ink jet recording method, it is attempted to stabilize the volumes of flying ink droplets. Thus, droplets each having extremely small amount of ink can be discharged at high speed, and the enhancement of durability of heater is attempted by eliminating the cavitation generated at the time of bubble extinction, among some other improvements that have been made possible. As a result, it becomes easier to obtain highly precise images in a better condition. In accordance with the specifications of the aforesaid Japanese Patent Applications, the structure arranged to enable bubbles to be communicated with the air outside is such that the shortest distance between the electrothermal converting element and discharge port is made significantly smaller than the conventional art.
Now, the description will be made of the conventional liquid discharge head of the kind. The conventional liquid discharge head is provided with an element base plate having the electrothermal converting element for discharging ink, and the orifice base plate bonded to the element base plate so as to form ink flow path. The orifice base plate is provided with plural discharge ports for discharging ink droplets; plural nozzles that enable ink to flow; and the ink supply chamber to supply ink to each of these nozzles. The nozzle is structured with the bubbling chamber where bubble is generated in ink retained therein by means of the electrothermal converting element, and the supply path for supplying ink to this bubbling chamber. For the element base plate, it is arranged to position the electrothermal converting element in the bubbling chamber. Also, there is arranged for the element base plate the supply port for supplying ink to the supply chamber from the backside of the main face adjacent to the orifice base plate. Then, for the orifice base plate, the discharge port is arranged in the position facing the electrothermal converting element on the element base plate.
For the conventional liquid discharge head structured as described above, ink is supplied from the supply port into the supply chamber along each of the nozzles, and filled in the bubbling chamber. Ink filled in the bubbling chamber is caused to fly in the direction almost orthogonal to the main surface of the element base plate by means of the bubble, which is generated when ink is given film boiling by the electrothermal converting element. Thus, ink is discharged from the discharge port as ink droplet.
Then, higher speed recording should be considered for the recording apparatus provided with the aforesaid liquid discharge head in order to attempt the higher quality output of images, the higher quality of recorded images, the output of higher resolution, and the like. To attain the high-speed recording, it has been attempted to increase the discharge frequency of ink droplets to fly from each of the nozzles of the liquid discharge head, that is, to increase the frequency of discharges, such as disclosed in the specifications of U.S. Pat. Nos. 4,882,595, and 6,158,843.
Particularly, in the specification of U.S. Pat. No. 6,158,843, the structure is proposed for the improvement of ink flow from the supply port to the supply path with the arrangement of the space that enables the ink flow path to be narrowed locally or with the arrangement of extruded-fluid resistive element in the vicinity of the supply port.
Nevertheless, in the conventional liquid discharge head described above, part of ink filled in the bubbling chamber is pushed back unavoidably to the supply path when ink droplet is discharged by the developed bubble in the bubbling chamber. As a result, the conventional liquid discharge head is encountered with the drawback that the discharge amount of ink droplet tends to be reduced along with the reduction of the volume of ink in the bubbling chamber.
Also, in the conventional liquid discharge head, part of pressure exerted on the developing bubble on the supply path side is allowed to escape to the supply path side or pressure loss takes place due to friction between the bubble and the inner walls of the bubbling chamber when part of ink filled in the bubbling chamber is pushed back to the supply path. As a result, the conventional liquid discharge head is encountered with a problem that the discharge speed of ink droplet is reduced along the reduction of bubble pressure.
Also, for the conventional liquid discharge head, there is a problem that the volume of small amount of ink filled in the bubbling chamber is caused to vary due to the bubble that is developed in the bubbling chamber, and therefore, the discharge amount of ink droplet is caused to vary accordingly.